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29
votes
4answers
6k views

How is it possible that the energy needed to stop a train is the same as the (chemical) energy in a pack of chocolate cookies?

Today my friend told me something that blew my mind completely. He said: The energy necessary to stop a train is equal to the energy in a pack of cookies. How is that possible? Is he right? I'm ...
78
votes
6answers
9k views

Does a gun exert enough gravity on the bullet it fired to stop it?

My question is set in the following situation: You have a completely empty universe without boundaries. In this universe is a single gun which holds one bullet. The gun fires the bullet and the ...
0
votes
1answer
49 views

Looking at a falling person (vertically) from 60m to the surface, how much wind effect is going to be felt?

I am trying to work out horizontal ranges for a falling person from height (in 10m steps from 0m to 60m). I have used this site http://www.convertalot.com/ballistic_trajectory_calculator.html to ...
3
votes
1answer
98 views

How many tons of lead is needed to curve space 1 nanometer? [closed]

How many tons of lead is needed to curve space 1 nanometer?
0
votes
0answers
77 views

Can the curvature of space be measured using a swimming pool?

I read somewhere that if the center of mass of two twelve ton elephants was one meter apart then the space they curve would be one nanometer longer. (Though I doubt elephants come that dense) This ...
0
votes
1answer
83 views

Is Voyager 2 slowing down?

Voyager 2 will leave the dominating gravitational influence of the Sun for a region where other stars have comparable influence on the craft. By the time it gets that far away, how much will it have ...
15
votes
1answer
2k views

Can I move an oil tanker?

Let's say that I'm standing at the edge of a basin made of concrete. This basin is filled with salt water and a ship floats on the water close to the edge of the basin. The ship is neither anchored ...
10
votes
2answers
283 views

Would a rocky planet orbiting so close to a very hot star eventually vaporize?

I was thinking about the physics behind a hypothetical scenario where a planet the size and the mass of the Earth is orbiting so close to a very hot star and what the long-term fate of such a planet ...
27
votes
3answers
4k views

How many X-rays does a light bulb emit?

I read somewhere that most things1 emits all kinds of radiation, just very few of some kinds. So that made me wondering whether there is a formula to calculate how many X-rays an 100W incandescent ...
2
votes
2answers
100 views

Reaction due to gravity

There is a reaction to the gravity of the earth on us but the earth does not move due to its huge mass. But what if I combine the weight of all humans and other things on Earth? Is it not enough to ...
2
votes
3answers
223 views

How can I calculate whether a shelf is strong enough to support a falling cat?

I'm building some shelves for my cat to climb on. The highest position the cat will be is 2 meters above the next shelf. The cat has a mass of 6.5kg. The shelf has a maximum load of 20kg. Using ...
1
vote
0answers
22 views

Fermi's yield estimation of the Trinity Test [duplicate]

In Enrico Fermi's eyewitness account of the Trinity nuclear test in 1945, he gives a brief description of a method that he used to estimate the blast energy of the test: About 40 seconds after the ...
-3
votes
1answer
121 views

Is the sum of mass of all planets in our solar system is 40% the mass of the Sun? [closed]

According to Chandrasekhar Limit,the mass of an object can not exceed than 1.4 times the mass of the sun.But according to some other theories,the sun was very large at former times and earth and ...
-3
votes
2answers
105 views

Would a piece of paper look as big as a small bedroom to an atom?, or bigger? [closed]

This evening my six year old asked me "Would a piece of paper look as big as this room to an atom?, or bigger?" ('this room' being a small sized bedroom) A friend suggested it would probably ...
1
vote
1answer
154 views

How many days it takes to travel to Cygnus? [duplicate]

BACKSTORY I read today newspaper and made discovery of planet Cygnus (in news paper of course :v) that human can live there! The distance is 1400 Lightyear. Assuming I travel with the world fastest ...
10
votes
3answers
820 views

Can a building get taller at night?

UberFacts recently tweeted "Office buildings are taller at night—a 1,300-foot-tall skyscraper shrinks about 1.5 millimeters under the weight of 50,000 occupants." Is what they are saying valid? It ...
0
votes
1answer
93 views

Could a Jumbo Jet aircraft fly on paper wings?

My dad was an airline pilot and, during his training, his instructor told him that, in absolutely ideal conditions, (in practice obviously impossible) that the actual material composing the wing ...
-1
votes
2answers
4k views

How many atoms are there in our solar system?

Including all objects gravitationally bound to the Sun, how many atoms are there in our solar system?
1
vote
2answers
690 views

How easily can the Earth flip?

The recent media attention to sunspot activity (however warranted) reminds me of a question I had long ago. Given the angular momentum and the slight 'wobble' of the earth, and remembering the ...
1
vote
2answers
76 views

Saturn V horizontally attached to Earth

If the Saturn V rocket were attached to the ground facing in the opposite direction of the Earth's spin, would it in anyway slow the Earth's spin on its axis? How significant of an impact would it ...
17
votes
2answers
4k views

How big is a 1kW fire?

What is the size/scale of a wood fire that is producing 1kW? I'd like to improve my ability to conceptualize various power scales.
1
vote
1answer
312 views

Effects of relativity on New Horizons spacecraft

How much would an atomic clock on board the new horizons spacecraft drift in comparison to an atomic clock on the surface of the earth near the equator after the spacecraft's 10 year journey to Pluto? ...
1
vote
2answers
49 views

What conditions would allow planetary-sized objects to collide and remain intact?

I am modeling some off-the-wall scenarios to try out with a game engine. One idea is trying to make a planet where some weird catastrophic incident has creates a funny shaped planet. I'm hoping to ...
1
vote
2answers
856 views

Does body weight affect the speed when going downhill on a mountain bike?

We know heavier objects fall faster when dropped at certain height. I was wondering if I am going downhill on my mountain bike without any peddling, will I travel faster or slower because I am fat?
2
votes
0answers
67 views

What's the fastest you can slingshot from one black hole to another? [closed]

Let's say you have your spaceship orbiting around a black hole. Its orbital velocity is arbitrarily close to the speed of light (or you can just set it to c*0.99 if it makes it easier.) There is ...
1
vote
2answers
151 views

Reduction of Earth's rotation due to increase in humidity

I came to know that, moon is moving away from earth, resulting reduction of Earth's rotation. Similarly, if Earth's humidity increases, water vapor will be move up to the air from water sources, will ...
0
votes
1answer
112 views

Estimate the amount of atoms in the smallest speck of matter you can see with the naked eye [closed]

I am currently working through a physics text book at my own pace on Newtonian mechanics. I came across this question in the the chapter 1 problems and had a bit of trouble with it. My biggest issue ...
1
vote
3answers
165 views

Is it possible for man to break Earth into 2 parts? [closed]

Many countries have extreme devastating nuclear weapons. Also they have weapons in very large numbers. I want to ask that Is it possible for man to break earth into 2 parts with the help ...
0
votes
1answer
676 views

Terminal velocity of a steel ball in water [closed]

I am investigating on the terminal velocity of steel balls moving in water. I used the balls with different diameters, such as 3.17mm, 6.02mm, etc. And I used a full-filled 1L graduated cylinder. I ...
1
vote
1answer
71 views

How much energy is saved when using luggage with wheels? [closed]

How much energy is saved when using luggage with wheels as opposed to carrying the luggage? Thanks.
2
votes
1answer
260 views

Could one fire a bullet with sufficient speed to leave the Earth?

Consider a gun or rifle fired directly upwards. My original question was what speed would be required to escape the Earth. The escape velocity from the surface of the Earth is the classic $$v_e = ...
2
votes
2answers
194 views

Vehicle Driving off Cliff (Thelma and Louise movie)

What is the slowest speed at which a vehicle driven off a cliff can clear the cliff without catching its underside between the wheels? In the usual frictionless vacuum, this would appear to depend on ...
7
votes
1answer
231 views

Is it possible to remove the last block from a the lowest layer of a Jenga tower?

A while back, my brother and I had a discussion about the possibility of removing the last block from the lowest layer of a Jenga tower with the layer immediately above it having only one block in it ...
3
votes
1answer
186 views

Possible to make full loop on a swing only by “pumping legs”?

Is it possible to make a full $360^{\circ}$ loop on the type of swing in a children's playground if I power the swing only by "pumping" my legs? i.e. nobody pushes me?
1
vote
1answer
86 views

What is the acceleration due to Earth's rotational and orbital movements?

What are the accelerations due to earths spin and orbital motion around the sun? It must be negligible otherwise humans would have been feeling it, are there any instruments that can measure it? would ...
-1
votes
1answer
42 views

Calculating time dilation

I'm writing a science fiction story where the protagonist's experience requires long intervals between events. My plan is to put him/her/it on a spaceship between events at an appreciable percentage ...
3
votes
1answer
109 views

Energy required to “glass” a given area of a temperate planet's surface

In some science fiction, orbital bombardment is portrayed as being able to vitrify the soil, or even the underlying bedrock, of a targeted area. While this is certainly not out of the question for ...
0
votes
0answers
100 views

Determine the amount of energy used for baking a cake

Let's suppose we have a room of temperature $T_0$ with an oven of volume $V$, both filled with air of density $\rho$ and specific heat $c$. We need to bake a cake in the temperature $T_1$. Thus we ...
8
votes
3answers
772 views

Is it possible to produce gravitational waves artificially?

Why don't they make a ball with irregularities, say the size of a tennis ball, then spin it very rapidly, so it would produce gravitational waves like a spinning star with irregularities on it? Is ...
1
vote
2answers
77 views

Torque (in $Nm$) of a cyclist

We're discussing bicycles with a friend, and it came to safety, speed and power. Now the question we have is: how much torque do my legs provide to the bicycle? I'm no expert in physics sadly, and ...
0
votes
1answer
190 views

How many coils of a wire in an electromagnet would make 100 milliTeslas field? [closed]

This is a rather stupid question. I'm making a basic electromagnet using copper wire and an iron nail and need to make an electromagnetic feild roughly about 100 milliTeslas . Ill be using a gauge 6 ...
2
votes
1answer
65 views

Finding the expression for the time it takes for a water tank to be half empty

The problem is to find an expression for the time it takes for a cylindrical water tank is half empty. I am given that the water tank has a diameter of $D_0$ and a hight $H$. The water outlet is ...
5
votes
3answers
3k views

How hot can metal get in sunlight? [closed]

I will make some 5mm blackened steel letters for a building. Now, in the sunlight in summer, how hot can they get? EDIT: i want to place some LEDs on the back of the letters. now the question is if ...
3
votes
1answer
327 views

Calculating Kryptonian speed in the movie “Man of Steel”

This is my first question, so I'm not sure if this is the right place to ask but: How would you go about calculating the speed of Kryptonians in the movie Man of Steel (2013)? Specifically, I'm ...
0
votes
2answers
190 views

What should the length of my wire be in order to get a surface area of 10cm^2?

I would like to make a flat coil out of a steel wire that is $1.22 ~\text{mm}$ in thickness (or $1.22~\text{mm}$ in diameter). I wish to make the coil up the wire into a flat disk that has a surface ...
0
votes
1answer
38 views

An example on computing the density of a typical nucleus

An example from my text is as such: Compute the density of a typical nucleus, and find the resultant mass if we could manufacture a nucleus with a radius of 1cm. I will only provide a partial ...
13
votes
1answer
398 views

How hot would tritium water be?

I realize this is kind of a silly question, but if you have tritium water, with the tritium half life of 12.5 years, I expect it would be quite hot. (note, this is not a homework question, I'm just ...
4
votes
4answers
475 views

Dodging paintballs

I was recently watching The Matrix, and was considering the speed at which one needs to move to literally dodge a projectile. Now, in real life, it is impossible to dodge bullets as such a feat would ...
0
votes
2answers
110 views

Do inelastic or elastic collisions have any effect on a large bodies movement (like the Earth)

Recently read a question regarding the temperature of the CMB & one of the comments got me thinking... From what I understand, collisions between subatomic particles and objects out in ...
2
votes
1answer
177 views

When will the Earth stop rotating?

I looked up leap second in Wikipedia. It is a second added (usually) to clocks to keep them in sync with the atomic clock. It said that 25 leap seconds were added in the last 43 years and that none ...